Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Hydrocarbon is contaminant in desired hydrocarbon
Reexamination Certificate
1999-09-17
2001-05-29
Wood, Elizabeth D. (Department: 1755)
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
Hydrocarbon is contaminant in desired hydrocarbon
C502S325000, C502S332000, C502S333000, C502S339000, C502S527140, C585S258000, C585S259000, C585S271000, C585S273000, C585S275000
Reexamination Certificate
active
06239322
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a selective hydrogenation catalyst for transforming unsaturated diolefinic hydrocarbons to &agr;-olefinic hydrocarbons, in particular for the hydrogenation of diolefinic compounds to &agr;- olefinic compounds at rates of at least 1.5 times higher, normally at least 3 times higher or even 5 times higher than the rate of hydrogenation of &agr;-olefinic compounds to saturated compounds. The catalyst contains palladium and at least one element selected from tin and lead.
BACKGROUND OF THE INVENTION
The invention also concerns the preparation of such a catalyst, and a process for selective hydrogenation of diolefins to &agr;-olefins using the catalyst.
Hydrocarbon conversion processes, for example steam cracking, visbreaking, catalytic cracking and coking, are carried out at high temperatures to produce a wide variety of olefinic compounds such as ethylene, propylene, n-butene-1, n-butene-2 compounds, isobutene or pentenes, and diolefinic compounds such as 1,2-propadiene, 1,3-butadiene and other compounds with boiling points in the “gasoline” cut range and which can be olefinic or diolefinic. Such processes inevitably lead, however, to the formation of highly unsaturated compounds such as diolefins (for example 1,2-propadiene), also alkynes (for example acetylene, propyne, 1-butyne, etc.). Such compounds have to be eliminated to allow the different cuts from these processes to be used in the chemical industry or for polymerisation processes. As an example, the C
4
cut from steam cracking contains a high proportion of 1,3-butadiene, butene-1, butene-2 compounds and isobutene.
Conventionally, butadiene is separated from the olefinic cut, for example by extractive distillation in the presence of dimethylformamide or N-methylpyrrolidone. The olefinic cut thus obtained contains isobutane, isobutene, butene-1, butene-2 compounds, n-butane and 1,3-butadiene, the latter being in an amount which can be between 0.1% to 2% by weight.
If butadiene is not an upgraded product, the cut can be directly treated using catalyst in the presence of hydrogen to transform the butadiene into n-butenes.
If the butene-1 and isobutene are desired products, processes must be used which produce a large quantity of butene-1 and separate different compounds, such as selective hydrogenation of butadiene to butenes with a small amount of isomerisation of butene-1 to butene-2, or separation of the isobutene by etherification with methanol to produce methyl-tertiobutyl ether.
There is currently a large demand for butene-1. This compound is used as a monomer in the polymer industry. Such use necessitates almost complete hydrogenation of butadiene, the presence of which is only tolerated in amounts of less than 10 ppm by weight.
Attaining these low butadiene contents with conventional catalysts based on nickel or palladium means a reduction in the butene-1 content due to butane formation and isomerisation of butene-1 to butene-2. In order to inhibit isomerisation of butene-1 to butene-2 compounds, some bimetallic formulae comprising palladium and a different metal have been proposed. In particular, palladium-silver systems can be cited, such as those described in U.S. Pat. No. 4,409,410, or palladium-gold, palladium-zinc, palladium-copper, palladium-cadmium, or palladium-tin systems, such as those described in Japanese patent application JP-A-87/05 4540. Proposed solutions for limiting consecutive hydrogenation, and thus butene formation, are more limited. As described in the literature (see, for example, “Selective Hydrogenation Catalysts and Processes: Bench to Industrial Scale”, J. P. Boitiaux et al., in “Proceedings of the DGMK Conference”, 11-13 Nov. 1993, Kassel, Germany), the hydrogenation selectivity for converting highly unsaturated compounds (diolefins or acetylenic compounds) to olefins originates from considerable complexation of the unsaturated compound on the palladium, preventing the olefins from accessing the catalyst and thus preventing their transformation to paraffins. This is clearly illustrated in the publication cited above where 1-butyne is selectively transformed to butene-1 on a palladium based catalyst. However, it should be noted that the rate of hydrogenation is relatively low. When all of the acetylenic compound has been converted, butene-1 hydrogenation is carried out at a much higher rate than the hydrogenation of the acetylenic compound. This phenomenon is also encountered with selective hydrogenation of butadiene.
This phenomenon poses several problems in industrial units. Firstly, in order to meet specifications regarding butadiene in the olefinic cut, a large quantity of butene-1 is transformed to butene since when the residual concentration of butadiene is low, the hydrogenation rates of butadiene and butene-1 are close to each other. Developing a catalyst which can allow butadiene hydrogenation at a rate which is much higher than the rate of butene-1 hydrogenation, whether these compounds are alone or mixed, is thus very important. This corresponds to catalyst properties which allow hydrogenation with high rate constant ratios for the hydrogenation of butadiene over that of butenes.
The importance of such a catalyst is not limited to an increase in butene-1 selectivity but it can also allow better control of the hydrogenation process. In the event of minor local hydrogen distribution problems, using such a catalyst would not lead to high conversion of butenes to butene and would thus minimise the problems of high exothermicity linked to these poorly controlled hydrogenation reactions which would aggravate distribution problems.
To solve this problem, it was important to develop a hydrogenation catalyst which could hydrogenate 1,3-butadiene to butenes while inhibiting the isomerisation of butene-1 to butene-2 and which was less active for consecutive hydrogenation of butene-1 to butene.
SUMMARY OF THE INVENTION
We have now discovered that catalysts constituted by palladium and at least one element M selected from tin and lead, have a 1,3-butadiene to butene-1 hydrogenation rate which is at least one and a half times higher, usually 3 times higher or even 5 times higher than the rate of hydrogenation of butene-1 to butane, whether these compounds are hydrogenated mixed together or separately. Further, these catalysts can inhibit isomerisation of butene-1 to butene-2 compounds.
The aim of the invention is thus to provide a composition of matter which can hydrogenate diolefinic compounds to &agr;-olefinic compounds.
A further aim of the present invention is to provide a composition of matter which can produce a diolefins/&agr;-olefins hydrogenation rate ratio of at least 1,5:1.
A third aim of the present invention is to provide a composition of matter with good selectivity towards butene-1 with respect to all n-butenes during hydrogenation of 1,3-butadiene.
The invention thus provides a hydrogenation catalyst characterized in that it comprises particles of a porous support and, as active elements, palladium distributed at the periphery of the particles and at least one element M selected from tin and lead. By periphery is meant that at least 80% of the palladium is present in a volume at the periphery of the carrier beads (spherules or substantially cylindrical extrudates) delimited by a spherical or cylindrical surface of radius r
1
corresponding to the average radius of the carrier spherules or extrudates, and a spherical or cylindrical surface with radius r
2
which is at least equal to 0.8 r
1
, this same definition appearing in U.S. Pat. No. 5,648,576 and divisional U.S. Pat. No. 5,889,187 wherein coinventors Didillon and Cameron of this application are also coinventors of the aforesaid patents.
Preferably, a proportion of at least 80% of the palladium is comprised in the volume of the particles (for example spherules and extrudates) constituting the catalyst within a depth of 500 &mgr;m, as shown in the following cross sectional diagram:
The palladium content in the catalyst is in the range 0.025% to 1.0% by weight, prefer
Cameron Charles
Didillon Blaise
Gautreau Christophe
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Wood Elizabeth D.
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